The present invention relates to an image forming apparatus.
So far, the image forming apparatus that is capable of performing image formation in both of a color mode and a monochromatic mode has been known. In such an image forming apparatus, there is an image forming apparatus, which is capable of changing a position of a transfer conveyance belt at the time of standby in order to prevent a first copy out time from becoming long, the first copy out time being a period of time from the time when a command of image formation is issued until the image formation is completed. Concretely, when the usage frequency of a color mode is high, the transfer conveyance belt will be made to be in a standby state in the color mode with reference to the past usage history of this image forming apparatus. When the usage frequency of a monochromatic mode is high, the transfer conveyance belt will be put to a standby state in the monochromatic mode. Further, this image forming apparatus is capable of setting the apparatus to a standby state in the color mode, to a standby state in the monochromatic mode or to a middle standby state as a default configuration (refer to Unexamined Japanese Patent Application Publication No. 2000-310922).
Here, in the image forming apparatus of the conventional tandem system, since a phase of each photoreceptor drums of yellow, magenta, cyan and black deviates after the end of the image formation in the monochromatic mode, a phase adjusting process is performed. Thereby, when there is a command of image formation in a color mode, since the phase adjusting process has been completed, the image formation in a color mode can be quickly performed, and the extension of the first copy out time has been prevented.
However, when the conventional image forming apparatus is arranged to be in a standby state while stopping a photoreceptor drum in the state that a phase adjustment has been completed, it will become the causes of image blur caused by ozone and image deterioration due to humidity. Thus, it is possible to perform a slight rotation of the photoreceptor drum to regulate the image blur caused by ozone and the image deterioration due to humidity. When the slight rotation is performed, the image blur caused by ozone and the image deterioration due to humidity can be regulated. However, since the phase deviation occurs due to the difference of load of each motor, which operates each of the photoreceptor drum of yellow, the photoreceptor drum of magenta, the photoreceptor drum of cyan and the photoreceptor drum of black, it is necessary to perform the phase adjusting process again.
As described above, although the phase adjustment is performed in the conventional image forming apparatus so as to shorten the first copy out time, neither the image blur caused by ozone nor the image deterioration due to humidity can be regulated. When slight rotation is performed to prioritize the regulation of the image blur caused by ozone and the image deterioration due to humidity, it is necessary to perform the phase adjusting process again. Therefore, it will become the cause of the extension of the first copy out time.